Main objectives in studying these defective human parvoviruses (AAV) are to (1) define specific biochemical mechanisms used in synthesizing their DNA, RNA and proteins, (2) identify and characterize the helper virus-mediated step(s) required for their replication and (3) relate biochemical findings to normal cellular processes as well as to potentials for selection interference with both AAV and Helper virus (adenoviruses, herpesviruses) infection. Among the methods used are nucleic acid hybridizations, analytical and preparative sucrose and CsCl sedimentations, molecular cleavage with restriction nucleases, gel electrophoresis, electron microscopy, DNA transfection, DNA cloning and microinjection of cells.